I wasn't sure if the market had to be configured first, or if there should be default entries.
Screenshot is from my server, but I tested in single player and both were empty.

https://i.imgur.com/Cfe1J0R.png

Is there any errors printed in chat on joining the world?

https://hastebin.com/abijoduhiq.css

None were printed in chat. Just in the console.

Just noticed this one... https://hastebin.com/bupividifa.bash